This invention relates to communication switching systems for selectively establishing two-way communication paths between desired ones of a set of telephone instruments, trunk line interfaces or other two-way communication peripheral devices, and deals more particularly with such a switching system of the type commonly referred to as a private automatic branch exchange (PABX) for servicing a reasonably large number of telephone instruments or other two-way communication peripheral devices, for example up to several hundred of such devices, such as those used in a given office, factory, government agency or similar business establishment.
The communication system of this invention is in many respects similar to that disclosed in copending U.S. patent application Ser. No. 665,551, filed Mar. 10, 1976. The communication system of that application is one using time division multiplexing for the transmission of signals on the communication lines and has a processor implemented common control. Further, the system disclosed in the application may be said to be one having, for the transmission of signals between peripheral devices, a single highway pair consisting of a single send highway to which the peripheral devices have sending access and a single receive highway to which the peripheral devices have receiving access. In such system, the number of peripheral devices is limited by the number of time slots made available by the multiplexing format. In the particular system shown by the application a maximum of 50 two-way communication peripheral devices can be serviced.
The general object of this invention is to provide a communication switching system comprised of a number of highway pairs, each generally similar to the single highway pair of the aforesaid patent application, whereby an increased number of peripheral devices may be included in the system.
Another object of this invention is to provide a communication switching system of the foregoing character whereby the size of the system, measured by peripheral device capacity, is flexible and may be readily varied incrementally by varying the number of highway pairs included in the system.
A still further object of the invention is to provide a multiple highway communication system which utilizes many of the same components as the single highway pair system of the aforesaid patent application and which system has or is capable of having the same desirable features as said single highway pair system, these features including a low per station cost for the system, ease in installing and maintaining the system, speedy operation in setting up and disconnecting communication paths and handling other services requests, and the ability to provide various different system functions, such as camp-on, call forwarding, call conferencing, call hold, etc. largely through programming of the processor memory and without the need for keys on the telephone instruments.
Other objects and advantages of the invention will be apparent from the drawings and from the following detailed description and claims.